The proper function of all the components and structural parts in the hydraulic pressure area of an, in particular hydraulically driven, membrane pump has a decisive effect on the displacement as well as on the dosing precision of such a pump.
Other structural parts of the membrane pump, such as the leakage compensation valve as well as the pressure-limiting valve, are liquid-tight in new condition and have no leakage.
In contradistinction thereto, the piston sealing is not liquid-tight even in new condition. Thus, depending on the embodiment of the sealing, the hydraulic fluid, and the operating parameters such as pressure, temperature, etc., there is in operation always a certain leakage which is then filled once again in the rear dead point of the piston, i.e. at the end of the intake stroke, by the leakage compensation valve.
Even if a gas discharge valve is customarily installed on the membrane pump, a certain leakage results in this valve. Moreover, all of said structural parts of the membrane pump are subjected to a certain wear in operation. This likewise makes itself noticeable by an increased leakage which has a disadvantageous effect on the displacement as well as on the dosing precision. Also an undesired increase in leakage can occur due to the failure of a seal, in particular in the area of the pump piston.
In practice, it has been previously attempted to address this problem by promptly exchanging, based on experience, the structural parts in question, which are subject to wear. Despite this, it happens relatively frequently that structural parts fail prematurely and thus cause undesirable subsequent damage which is undesirable due to the necessary interruption of operation.
In order to determine any leakage occurring in the hydraulic pressure area of the membrane pump, it has been attempted previously to make this known promptly via the pump's deficiency in displacement which occurs or by means of temperature measurement. These processes have, however, not proven themselves effective since they either are associated with too great an expense in construction or do not produce the desired results.